CN107001712B - Pneumatic tire - Google Patents

Abstract

The present invention provides a pneumatic tire having a tread made of a rubber composition capable of greatly improving high wet grip performance, dry grip performance and durability while maintaining a good balance therebetween. A pneumatic tire having a tread made of a rubber composition containing 90 mass% or more of a diene rubber per 100 mass% of a rubber component, the rubber composition further containing a hydrogenated terpene aromatic resin obtained by hydrogenating a double bond of the terpene aromatic resin, the hydrogenated terpene aromatic resin having a degree of hydrogenation of the double bond of 5 to 100% and a hydroxyl value of 20mg KOH/g or less, the hydrogenated terpene aromatic resin being contained in an amount of 1 to 50 parts by mass per 100 parts by mass of the diene rubber, the rubber composition further containing 1 to 70 parts by mass of a specific inorganic filler per 100 parts by mass of the diene rubber.

Description

Pneumatic tire

Technical Field

The present invention relates to a pneumatic tire having a tread formed of a rubber composition.

Background

It is known that the grip performance of a rubber composition for a tread can be improved by blending α -methyl styrene-based resin, particularly the wet grip performance (see, for example, patent document 1).

In order to improve dry grip performance, it is necessary to improve tan δ at 20 ℃. Unfortunately, this also leads to an increase in tan δ at 30 to 70 ℃ as an indicator of rolling resistance, and therefore this is undesirable. For example, known methods include the use of korein, coumarone-indene resins, styrene acrylic resins, and the like; however, these methods also result in greatly increased rolling resistance and are therefore difficult to use in fuel economy critical applications.

Generally, a resin for improving grip performance (grip resin) functions to increase viscoelasticity and hysteresis loss of rubber, particularly tan δ. In addition, these resins also function to increase the adhesion between the tread and the road surface because they bloom to the tread surface during running, forming an adhesive blooming layer together with the processing oil, the polymer decomposition products, the low molecular weight organic materials and other components. The above-described effects combine to contribute to improvement in grip performance.

List of cited documents

Patent document

Patent document 1: JP 2013-1805A

Disclosure of Invention

Technical problem

As described above, various attempts have been made to improve grip performance, but none has achieved a high level of balanced improvement in wet grip performance, dry grip performance and durability.

The present invention is intended to solve the above-mentioned problems and provide a pneumatic tire having a tread formed of a rubber composition capable of greatly improving wet grip performance, dry grip performance and durability while maintaining a good balance therebetween.

Technical scheme for solving problems

The present invention relates to a pneumatic tire having a tread made of a rubber composition containing a rubber component containing 90 mass% or more of a diene rubber based on 100 mass% of the rubber component, the rubber composition further containing a rubber obtained by copolymerizing double bonds of a terpene aromatic resinA hydrogenated terpene aromatic resin obtained by hydrogenation, the hydrogenated terpene aromatic resin having a degree of double bond hydrogenation of 5 to 100% and a hydroxyl value of 20mgKOH/g or less, the hydrogenated terpene aromatic resin being contained in an amount of 1 to 50 parts by mass per 100 parts by mass of a diene rubber, the rubber composition further containing a nitrogen adsorption specific surface area of 10 to 120m²(ii) an inorganic filler comprising at least one selected from the group consisting of a compound represented by the following formula, magnesium sulfate and silicon carbide,

the content of the inorganic filler is 1 to 70 parts by mass relative to 100 parts by mass of the diene rubber,

mM·xSiO_y·zH₂O

wherein M represents at least one metal selected from the group consisting of Al, Mg, Ti, Ca and Zr, or an oxide or hydroxide of the metal; m represents an integer of 1 to 5, x represents an integer of 0 to10, y represents an integer of 2 to 5, and z represents an integer of 0 to 10.

The inorganic filler is preferably aluminum hydroxide.

The softening point of the hydrogenated terpene aromatic resin is preferably from 80 ℃ to 180 ℃, more preferably from 114 ℃ to 160 ℃.

The hydroxyl value of the hydrogenated terpene aromatic resin is preferably 0mg KOH/g.

The diene rubber preferably contains 60% by mass or more of a styrene-butadiene rubber having a styrene content of 19% by mass to 60% by mass.

Advantageous effects of the invention

The pneumatic tire of the present invention has a tread made of a rubber composition. The rubber composition contains: a rubber component containing 90% by mass or more of a diene rubber; a hydrogenated terpene aromatic resin obtained by hydrogenating a double bond of a terpene aromatic resin, the hydrogenated terpene aromatic resin having a degree of hydrogenation of the double bond of 5 to 100% and a hydroxyl value of 20mg KOH/g or less; and a specific inorganic filler having a predetermined nitrogen adsorption specific surface area. The rubber composition contains 1 to 50 parts by mass of a hydrogenated terpene aromatic resin and 1 to 70 parts by mass of an inorganic filler per 100 parts by mass of a diene rubber. The present invention provides such a pneumatic tire that achieves a high level of balance improvement in wet grip performance, dry grip performance, and durability.

Detailed Description

The pneumatic tire of the present invention has a tread made of a rubber composition. The rubber composition contains: a rubber component containing 90% by mass or more of a diene rubber; a hydrogenated terpene aromatic resin obtained by hydrogenating a double bond of a terpene aromatic resin, the hydrogenated terpene aromatic resin having a degree of hydrogenation of the double bond of 5 to 100% and a hydroxyl value of 20mg KOH/g or less; and a specific inorganic filler having a predetermined nitrogen adsorption specific surface area. The rubber composition contains 1 to 50 parts by mass of a hydrogenated terpene aromatic resin and 1 to 70 parts by mass of an inorganic filler per 100 parts by mass of a diene rubber.

By adding a predetermined amount of a specific hydrogenated terpene aromatic resin together with a specific inorganic filler to a rubber composition containing a diene rubber, it is possible to maintain a good balance between wet grip performance, dry grip performance and durability while greatly improving them, as compared with the conventional method using a combination of a low softening point resin and a high softening point resin or adding a terpene-based resin or an aromatic resin that is well miscible with rubber.

This is because the degree of hydrogenation is 5 to 100%, and the hydrogenated terpene aromatic resin having a hydroxyl value of 20mg KOH/g or less has the following characteristics which can significantly achieve the above-described effects.

Since the hydrogenated terpene aromatic resin has a high degree of structural flexibility due to being hydrogenated, the resin can be bloomed quickly to the tread surface regardless of the molecular weight and the softening point thereof. In addition, the hydrogenated terpene aromatic resin having a reduced amount of double bonds due to hydrogenation shows a greatly increased dispersibility in diene rubber while promoting crosslinking of the rubber without adsorbing sulfur of the crosslinking agent, thereby producing uniform crosslinking sites between rubber polymers, and thus improving the modulus of the vulcanized rubber composition. Furthermore, uniform and tight crosslinking of the rubber results in good durability and good resistance to foaming. Further, the hydrogenated terpene aromatic resin having a hydroxyl value of 20mg KOH/g or less shows low self-aggregating properties in the rubber, with the result that the Shore hardness (Hs) at room temperature is low and the high temperature Hs is maintained, or in other words, the temperature dependence of Hs is small.

The above effects are particularly remarkable when the rubber component includes a diene rubber.

It should be noted that generally, hydrogenating a resin may enhance its thermal stability and increase its shelf life. Therefore, when the hydrogenated terpene aromatic resin is blended into rubber, the progress of pyrolysis and oxidation is reduced, resulting in a reduction in odor.

Further, it is presumed that the addition of an inorganic filler having a predetermined nitrogen adsorption specific surface area such as aluminum hydroxide can provide the following effects (1) to (4), which allow the above-described effects (particularly, the effect of improving wet grip performance) to be significantly achieved.

(1) During the mixing, an inorganic filler such as aluminum hydroxide (Al (OH) is mixed in₃) May be partially converted into alumina (Al) having mohs hardness equal to or higher than that of silica₂O₃) Or an inorganic filler such as aluminum hydroxide is bonded to silica (by covalent bonding or dehydration) so that it is fixed by finely dispersed silica chains in the rubber compound. Such metal oxide lumps or inorganic fillers provide an anchoring effect to the micro-roughness (having a pitch of several tens of micrometers) of the aggregate on the road surface, thereby improving the wet grip performance.

(2) As a result of contact (friction) of silica on a road surface with an inorganic filler such as aluminum hydroxide on a tire surface during running, it can be considered that a covalent bond is formed immediately, thereby improving wet grip performance.

(3) On a wet road surface, a portion of the tire surface is in contact with the road surface through a film of water. Generally, such a water film is considered to be evaporated by frictional heat generated in an area where the tire directly contacts with a road surface. However, for example, when aluminum hydroxide is mixed, the frictional heat is considered to contribute to endothermic reaction of aluminum hydroxide on the tire surface (e.g., "Al (OH))₃→1/2Al₂O₃+3/2H₂O ″), resulting in reduced evaporation of the water film (moisture). If the water film evaporates, a void is formed between the tire surface and the road surface, and thus the road surface/tire contact area is reduced, resulting in a decrease in wet grip performance.

(4) When the above-described phenomenon (1) or (2) occurs, the inorganic filler particles vibrate at high frequency during running. Such high frequency vibration promotes blooming of the adhesive components (e.g., grip resin and liquid components) in the adjacent rubber compositions. As a result, the amount of the binder component around the inorganic filler particles is increased as compared with other portions not containing the inorganic filler, which improves wet grip performance.

The rubber composition of the present invention further improves dry grip performance by adding an inorganic filler such as aluminum hydroxide having a predetermined nitrogen adsorption specific surface area. In particular in driving tests, many professional drivers have made the following comments on the incorporation of inorganic fillers: the tread is in close contact with the road surface and exhibits behavior such as blooming of the grip resin to the surface. The reason for this may be as follows.

When a specific inorganic filler is mixed into the rubber composition, high tension is applied to the surface of the tread rubber, particularly during small radius rotation or drifting, which causes the tread rubber to vibrate at high frequency. When the high-frequency vibration reaches more than 1000Hz, (A) the grip resin and the adhesive component are bloomed to the interface between the inorganic filler and the rubber component, thereby promoting road grip; (B) preferably, the inorganic filler physically or chemically binds adjacent silica and carbon black so that large voids do not occur around the inorganic filler even during running; and (C) an inorganic filler in the form of fine particles having a predetermined nitrogen adsorption specific surface area increases hysteresis of the rubber composition. These effects are believed to contribute to the improvement of dry grip performance.

Although wet grip performance can be improved by the effect caused by the addition of a conventional inorganic filler such as aluminum hydroxide, abrasion resistance, wear appearance after abrasion, or other properties are generally deteriorated in this case. Therefore, it is difficult to achieve a balanced improvement in these properties. In the present invention, since an inorganic filler such as aluminum hydroxide having a predetermined nitrogen adsorption specific surface area is combined with a specific hydrogenated terpene aromatic resin, it is possible to greatly improve the wet grip performance, the dry grip performance and the durability while maintaining a good balance therebetween.

The rubber component of the rubber composition of the present invention contains a diene rubber. The use of diene rubbers in the rubber component provides good grip properties.

The term "grip performance" when used alone in the present invention is a generic term that includes wet grip performance and dry grip performance.

Any diene rubber may be used, and examples thereof include isoprene-based rubbers such as Natural Rubber (NR), high-purity natural rubber (UPNR), deproteinized natural rubber (DPNR), Epoxidized Natural Rubber (ENR) and polyisoprene rubber (IR), styrene-butadiene rubber (SBR), polybutadiene rubber (BR), styrene-isoprene-butadiene rubber (SIBR), Chloroprene Rubber (CR) and acrylonitrile butadiene rubber (NBR). Among them, for a tire used in a passenger car, the diene rubber preferably must contain SBR in terms of grip performance. More preferably NR, SBR and/or BR, still more preferably SBR and/or BR, wherein a combination of SBR and BR is particularly preferred. For use in tires for trucks and buses having a high ground contact pressure per unit area, the diene rubber is preferably based on NR excellent in both tensile strength and tear strength.

Any styrene-butadiene rubber (SBR) may be used, and examples thereof include emulsion polymerized SBR (E-SBR) and solution polymerized SBR (S-SBR), all of which may or may not be oil-extended. In particular, oil-extended high molecular weight SBR is preferable in view of grip performance. Modified SBR' S that exhibit enhanced interaction with fillers, such as chain end modified or backbone modified S-SBR, may also be used. These types of SBR may be used alone, or two or more thereof may be used in combination.

The modified SBR may be preferably coupled with tin, silicon, or the like. The modified SBR may be prepared by a coupling reaction according to a conventional method, for example, by reacting an alkali metal (e.g., Li) or an alkaline earth metal (e.g., Mg) in the molecular chain end of the modified SBR with a tin halide, a silicon halide, or the like.

The modified SBR may also preferably be a copolymer of styrene and butadiene containing a primary amino group or an alkoxysilyl group. The primary amino group may be bound to the initiating end, terminating end, backbone or side chain of the polymer. The primary amino group is preferably introduced into the initiating or terminating end of the polymer, as this can reduce energy loss at the polymer chain end, thereby improving hysteresis loss properties.

The modified SBR may be suitably obtained, in particular, by modifying the polymerization terminal (active terminal) (S-SBR) of a solution-polymerized styrene-butadiene rubber (S-SBR) with a compound represented by the following formula (3) (modified S-SBR (modified SBR disclosed in JP2010-111753 a)). In this case, the molecular weight of the polymer can be easily controlled, and thus the content of the low molecular weight component capable of increasing tan δ can be reduced. In addition, the bond between the silica and the polymer chain can be reinforced to further improve wet grip performance and other properties.

In the formula (3), R¹¹，R¹²And R¹³The same or different from each other, each represents an alkyl group, an alkoxy group (preferably an alkoxy group of C1-C8, more preferably C1-C6, more preferably C1-C4), a siloxy group, an acetal group, a carboxyl group (-COOH), a mercapto group (-SH), or a derivative thereof; r¹⁴And R¹⁵Identical to or different from each other, each represents a hydrogen atom or an alkyl group (preferably a C1-C4 alkyl group). n represents an integer (preferably 1 to 5, more preferably 2 to 4, and further preferably 3).

R¹¹，R¹²And R¹³Each of which is preferably an alkoxy group, R¹⁴And R¹⁵Each of which is preferably a hydrogen atom. This can provide excellent wet grip performance, fuel economy and handling stability.

Specific examples of the compound of formula (3) include 3-aminopropyltrimethoxysilane, 3-aminopropyldimethylmethoxysilane, 3-aminopropylmethyldimethoxysilane, 2-dimethylaminoethyltrimethoxysilane, 3-diethylaminopropyltrimethoxysilane and 3- (N, N-dimethylamino) propyltrimethoxysilane. These may be used alone or in combination of two or more.

Modification of the styrene-butadiene rubber with the compound (modifier) of the formula (3) can be carried out by a conventional method, for example, those disclosed in JP H06-53768B, JP H06-57767B and JP 2003-514078T. For example, the modification can be carried out by contacting styrene-butadiene rubber with a modifier. Examples thereof include a method in which, after synthesizing styrene-butadiene rubber by anionic polymerization, a predetermined amount of a modifier is added to a polymer rubber solution to react the polymerized end (living end) of the styrene-butadiene rubber with the modifier, or a method in which a modifier is added to a styrene-butadiene rubber solution to react them.

The styrene content of SBR is preferably 19% by mass or more, more preferably 21% by mass or more, still more preferably 25% by mass or more, and particularly preferably 30% by mass or more. The styrene content is also preferably 60% by mass or less, more preferably 55% by mass or less, still more preferably 50% by mass or less, and particularly preferably 45% by mass or less. When the styrene content is less than 19 mass%, insufficient grip performance may be obtained, and when the styrene content is more than 60 mass%, styrene groups may be adjacent to each other, so that the polymer becomes too hard and non-uniform crosslinking is more likely to occur, resulting in deterioration of durability. Further, the temperature dependence tends to increase, so that the obtained performance is more largely changed with respect to the temperature change, resulting in poor wet grip performance or dry grip performance.

Styrene content of SBR used in the present invention is determined by¹H-NMR analysis.

The vinyl group content of SBR is preferably 10 mass% or more, more preferably 15 mass% or more, further preferably 20 mass% or more, and particularly preferably 25 mass% or more. When the vinyl content is less than 10 mass%, sufficient grip performance cannot be obtained. The vinyl group content is preferably 90% by mass or less, more preferably 80% by mass or less, still more preferably 70% by mass or less, and particularly preferably 60% by mass or less. When the vinyl group content is more than 90 mass%, such SBR is difficult to prepare, and the yield thereof may be unstable. In addition, the rubber strength of this SBR is reduced, so that the performance is unstable.

The vinyl content (content of 1, 2-butadiene unit) of the SBR used in the present invention can be measured by infrared absorption spectrometry.

The glass transition temperature (Tg) of SBR is preferably-45 ℃ or more, more preferably-40 ℃ or more. The Tg is preferably 10 ℃ or less, more preferably 5 ℃ or less, and still more preferably 0 ℃ or less.

The glass transition temperature of SBR used in the present invention is measured by Differential Scanning Calorimetry (DSC) at a temperature rising rate of 10 ℃/min in accordance with JIS K7121.

The weight average molecular weight (Mw) of SBR is preferably 200000 or more, more preferably 250000 or more, and further preferably 300000 or more. For use in racing tires or high-wear tires, Mw is particularly preferably 1100000 or more. The Mw is also preferably 2000000 or less, more preferably 1800000 or less. The use of SBR having Mw of 200000 or more provides higher grip performance, fuel economy and durability. Whereas Mw exceeding 2000000 may result in poor filler dispersibility and deteriorated durability.

Here, the weight average molecular weight of SBR can be obtained by Gel Permeation Chromatography (GPC) (GPC-8000 series, available from Tosoh corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M available from Tosoh corporation), calibrated with polystyrene standards.

For a tire for passenger cars, the amount of SBR is preferably 60 mass% or more, more preferably 65 mass% or more, and further preferably 70 mass% or more, based on 100 mass% of the diene rubber. When it is less than 60% by mass, the grip performance tends to be insufficient. The upper limit of the amount of SBR is not particularly limited, and may be 100 mass%, but is preferably 90 mass% or less, and more preferably 80 mass% or less.

In particular, the diene rubber preferably contains 60% by mass or more of SBR having a styrene content of 19% by mass to 60% by mass, more preferably 65% by mass or more of SBR having a styrene content of 25 to 55% by mass. In this case, higher grip performance and higher durability can be achieved.

Any polybutadiene rubber (BR) may be used, including, for example, high cis content BR such as BR1220 available from Zeon corporation and BR130B and BR150B available from Udo Kyoho; modified BR such as BR1250H available from Zeon corporation; BR comprising syndiotactic polybutadiene crystals, such as VCR412 and VCR617 both available from Utsu Hippon; and BR synthesized using rare earth catalysts, such as BUNA-CB25 from Lanxess. These types of BR may be used alone, or two or more thereof may be used in combination. Among them, BR synthesized using a rare earth catalyst (rare earth catalyzed BR) is preferable in view of abrasion resistance and fuel economy.

The term "rare earth catalyzed BR" refers to polybutadiene rubber synthesized using rare earth catalysts, characterized by a high cis content and a low vinyl content. The rare earth catalyzed BR may be BR commonly used in tire production.

Rare earth catalysts for synthesizing rare earth catalyzed BR may be known. Examples thereof include catalysts containing lanthanide rare earth compounds, organoaluminum compounds, aluminoxanes or halogen-containing compounds, optionally with lewis bases. Among them, a neodymium (Nd) catalyst containing a Nd-containing compound as a lanthanoid rare earth compound is particularly preferable.

Examples of lanthanide rare earth compounds include halides, carboxylates, alkoxides, thioalkoxides, and amides of rare earth metals having atomic numbers of 57 to 71. Among them, the above-mentioned Nd catalyst is preferable because it gives BR having a high cis content and a low vinyl content.

Examples of the organoaluminum compound include compounds represented by the following formula: AlR^aR^bR^cWherein R is^a，R^bAnd R^cAre the same or different from each other, and each represents a hydrogen atom or a C1-C8 hydrocarbon group. Examples of the aluminoxane include non-cyclic aluminoxane and cyclic aluminoxane. Examples of the halogen-containing compound include aluminum halides represented by the following formula: AlX_kR^d _3-kWherein X represents a halogen atom, R^dRepresents C1-C20 alkyl, aryl or aralkyl, k is 1, 1.5, 2 or 3; strontium halides such as Me₃SrCl，Me₂SrCl₂，MeSrHCl₂And MeSrCl₃(ii) a Metal halides such as silicon tetrachloride, tin tetrachloride and titanium tetrachloride. Lewis bases may be used for the complexation of lanthanide rare earth compounds, which are suitableExamples of (b) include acetylacetone, ketones and alcohols.

In the polymerization of butadiene, the rare earth catalyst may be used in a solution of an organic solvent (e.g., n-hexane, cyclohexane, n-heptane, toluene, xylene or benzene), or may be supported on a suitable carrier such as silica, magnesium oxide or magnesium chloride. As for the polymerization conditions, the polymerization may be solution polymerization or bulk polymerization, preferably at a polymerization temperature of-30 ℃ to 150 ℃, and the polymerization pressure may be appropriately selected depending on other conditions.

The cis-1, 4-bond content (cis content) of rare earth-catalyzed BR is preferably 90 mass% or more, more preferably 93 mass% or more, and further preferably 95 mass% or more. If the cis content is less than 90 mass%, the durability or abrasion resistance tends to deteriorate.

The vinyl content of the rare earth-catalyzed BR is preferably 1.8 mass% or less, more preferably 1.5 mass% or less, still more preferably 1.0 mass% or less, and particularly preferably 0.8 mass% or less. If the vinyl content is more than 1.8 mass%, the durability or abrasion resistance tends to deteriorate.

The vinyl content (content of 1, 2-butadiene units) and cis content (cis-1, 4-bond content) of the BR used in the present invention can be determined by infrared absorption spectroscopy.

When BR is blended, the amount of BR is preferably 10 mass% or more, more preferably 15 mass% or more, and further preferably 20 mass% or more, based on 100 mass% of the diene rubber. The amount of BR is also preferably 70% by mass or less, more preferably 60% by mass or less. For use in a tire requiring grip performance, it is preferably 40% by mass or less. When the BR is less than 10 mass% or more than 70 mass%, the abrasion resistance, grip performance or fuel economy tends to be insufficient.

Examples of NRs include those commonly used in the tire industry, such as SIR20, RSS #3, and TSR 20.

For tires for trucks and buses, the amount of NR is preferably 60 to 100% by mass based on 100% by mass of the diene rubber, and for tires for passenger cars or commercial vehicles, the amount of NR is preferably 0 to 70% by mass based on 100% by mass of the diene rubber. When the amount of NR is outside the above range, sufficient grip performance, abrasion resistance or durability cannot be obtained.

The rubber component may include other rubbers in addition to the diene rubber. Examples of other rubbers include butyl rubber (IIR).

The amount of the diene rubber is 90% by mass or more, preferably 95% by mass or more, based on 100% by mass of the total amount of the rubber components including other rubbers. The upper limit of the amount is not particularly limited, and may be 100 mass%.

The rubber composition of the present invention contains a hydrogenated terpene aromatic resin obtained by hydrogenating the double bond of a terpene aromatic resin. The hydrogenated terpene aromatic resin has a degree of double bond hydrogenation of 5 to 100% and a hydroxyl value of 20mg KOH/g or less.

The term "terpene aromatic resin" used in the hydrogenation of a terpene aromatic resin means a compound obtained by copolymerizing an aromatic compound and a terpene compound by a conventional method. In particular, the compounds may be prepared, for example, by reacting a compound such as BF₃In any order, to an organic solvent such as toluene and reacting the mixture at a predetermined temperature for a predetermined time.

The copolymerization ratio between the aromatic compound and the terpene compound can be appropriately selected so that the resulting hydrogenated terpene aromatic resin has physical properties as described later. The terpene aromatic resin may contain a copolymerized unit other than the aromatic compound and the terpene compound, such as indene, as long as the resulting hydrogenated terpene aromatic resin has the physical properties described later.

The aromatic compound may be any compound having an aromatic ring, and examples thereof include phenol compounds such as phenol, alkylphenol, alkoxyphenol and unsaturated hydrocarbon group-containing phenol; naphthol compounds such as naphthol, alkylnaphthol, alkoxynaphthol and naphthol containing unsaturated hydrocarbon group; and styrene derivatives such as styrene, alkylstyrene, alkoxystyrene and styrene containing unsaturated hydrocarbon group, preferably styrene derivatives. The alkyl group or alkoxy group in the aforementioned compounds each preferably has 1 to 20 carbon atoms, more preferably 1 to12 carbon atoms. The unsaturated hydrocarbon groups in the above compounds each preferably have 2 to 20 carbon atoms, more preferably 2 to12 carbon atoms.

The aromatic compound may have one substituent or two or more substituents on the aromatic ring. In the case of an aromatic compound having two or more substituents on the aromatic ring, the substituents may be located at any of the ortho-position, meta-position or para-position. Further, in the case of a styrene derivative having a substituent on an aromatic ring, the substituent may be at the ortho, meta or para position with respect to the vinyl group of styrene.

The aromatic compounds may be used alone or in combination of two or more.

Specific examples of the alkylphenol include methylphenol, ethylphenol, butylphenol, tert-butylphenol, octylphenol, nonylphenol, decylphenol and dinonylphenol. They may have corresponding substituents in any of the ortho, meta or para positions. Among them, tert-butylphenol is preferable, and p-tert-butylphenol is more preferable.

Specific examples of the alkylnaphthol include compounds obtained by replacing the phenol moiety of the alkylphenol with naphthol.

Specific examples of the alkylstyrene include compounds obtained by replacing the phenol moiety of the alkylphenol with styrene.

Specific examples of the alkoxyphenol include compounds obtained by substituting the alkyl group of the alkylphenol with a corresponding alkoxy group. Specific examples of alkoxynaphthols include compounds obtained by substituting the alkyl group of an alkylnaphthol with the corresponding alkoxy group. Specific examples of the alkoxystyrene include compounds obtained by substituting the alkyl group of the alkylstyrene with a corresponding alkoxy group.

Examples of the unsaturated hydrocarbon group-containing phenol include compounds containing at least one hydroxyphenyl group per molecule, and in which at least one hydrogen atom of the phenyl group is substituted with an unsaturated hydrocarbon group. The unsaturated bond in the unsaturated hydrocarbon group may be a double bond or a triple bond.

Examples of unsaturated hydrocarbon groups include C2-C20 alkenyl groups.

Specific examples of the unsaturated hydrocarbon group-containing phenol include isopropenylphenol and butenylphenol. Specific examples of the naphthol having an unsaturated hydrocarbon group and the styrene having an unsaturated hydrocarbon group are similarly described.

The terpene compound is represented by the formula (C)₅H₈)_nThe hydrocarbons or oxygen-containing derivatives thereof, each having a terpene skeleton, may be classified as monoterpenes (C)₁₀H₁₆) Sesquiterpenes (C)₁₅H₂₄) Diterpenes (C)₂₀H₃₂) And other terpenes. The terpene compound is not particularly limited, and is preferably a cyclic unsaturated hydrocarbon. The terpene compounds also preferably do not contain hydroxyl groups.

Specific examples of terpene compounds include α -pinene, β -pinene, 3-carene (delta-3-carene), dipentene, limonene, myrcene, alloocimene, ocimene, α -phellandrene, α -terpinene, gamma-terpinene, terpinolene, 1, 8-cineole, 1, 4-cineole, α -terpineol, β -terpineol, and gamma-terpineol, with α -pinene, β -pinene, 3-carene (delta-3-carene), dipentene, and limonene, and α -pinene or limonene being more preferred because they balance improved grip performance and durability.

These terpene compounds may be used alone or in combination of two or more.

Examples of the terpene aromatic resin prepared by, for example, copolymerization of a styrene derivative with limonene include compounds represented by the following formula (I):

wherein R as a substituent on the aromatic ring represents a C1-C20 alkyl group, a C1-C20 alkoxy group or a C2-C20 unsaturated hydrocarbon group, provided that the number of the substituent R may be 1 to 5, and when the number of the substituents is two or more, the substituents may be the same as or different from each other, or may be located at any position; m is 0.2-20; n is 2 to 10.

Specific examples of terpene aromatic resins include YS resin TO125, YS resin TO115, YS resin TO105, YS resin TO85, and YS polyester UH115, all available from Yasuhara Chemical co.

The hydrogenated terpene aromatic resin in the present invention can be produced by hydrogenating the double bonds of the above terpene aromatic resin by a usual method. The hydrogenation can be carried out, for example, by catalytic hydrogen reduction using noble metals such as palladium, ruthenium, rhodium or nickel as catalysts, alone or on supports such as activated carbon, activated alumina or diatomaceous earth.

The content of the catalyst is preferably 0.1 to 50% by mass, more preferably 0.2 to 40% by mass, based on 100% by mass of the starting terpene aromatic resin. When the amount of the catalyst is less than 0.1% by mass, the hydrogenation reaction tends to be slow, and when the amount thereof exceeds 50% by mass, the catalyst may remain as impurities, which can act as obstacles for dispersion of the filler or dispersion of the polymer, resulting in insufficient tensile strength or grip performance. The hydrogen pressure in the hydrogenation reaction is usually 5 to 200kg/cm²Preferably 50 to 100kg/cm². If the hydrogen pressure is less than 5kg/cm²The rate of hydrogenation reaction tends to be slowed down, whereas if the hydrogen pressure exceeds 200kg/cm²The reaction equipment may be damaged or become difficult to maintain, resulting in poor yield. The temperature of the hydrogenation reaction is usually 10 to 200 ℃ and preferably 20 to 150 ℃. If the reaction temperature is less than 10 ℃, the hydrogenation reaction tends to be slow, and if the reaction temperature exceeds 200 ℃, the reaction equipment may be damaged or become difficult to maintain, resulting in a deterioration in yield.

The hydrogenated terpene aromatic resin may be commercially available products such as YS polyester M80, YS polyester M105, YS polyester M115, and YS polyester M125, which are available from Yasuhara Chemical Co.

The hydrogenated terpene aromatic resin of the present invention prepared as above contains a hydrogenated double bond.

The hydrogenated terpene aromatic resin has a degree of hydrogenation of the double bond of 5 to 100%. In particular, the degree of hydrogenation of the double bond is preferably 6% or more, more preferably 7% or more, further preferably 8% or more, further preferably 11% or more, and particularly preferably 15% or more. The upper limit of the degree of hydrogenation of the double bond has not been precisely defined at present because the preferred range thereof may vary depending on factors associated with the hydrogenation reaction, such as progress in production techniques (e.g., heating and pressurizing conditions, catalyst) or improvement in yield. In the present case, the upper limit thereof is preferably 80% or less, more preferably 60% or less, further preferably 40% or less, further preferably 30% or less, and particularly preferably 25% or less. If the degree of hydrogenation is less than 5%, grip performance (particularly dry grip performance) or durability tends to be insufficient.

The degree of hydrogenation (hydrogenation rate) is determined by¹The integral of the double bond peak determined by H-NMR (proton NMR) was calculated by the following formula. The degree of hydrogenation (hydrogenation rate) herein means the percentage of double bonds hydrogenated.

(hydrogenation ratio (%)) ((a-B)/a) × 100

Wherein A: integration of double bond peaks before hydrogenation;

b: integration of double bond peaks after hydrogenation.

For example, when the terpene aromatic resin used is a compound of formula (I) obtained by copolymerization of a styrene derivative and limonene, a hydrogenated terpene aromatic resin represented by the following formula (II) will be obtained if the degree of hydrogenation is 100%, and a hydrogenated terpene aromatic resin represented by the following formula (III) will be obtained if the degree of hydrogenation is at least 5% but less than 100%, for example.

In the formula (II), R as a substituent on the cyclohexane ring represents a C1-C20 alkyl group, a C1-C20 alkoxy group or a C2-C20 unsaturated hydrocarbon group, provided that the number of the substituent R may be 1 to 5, and when the number of the substituents is 2 or more, the substituents may be the same as or different from each other, or may be located at arbitrary positions; m is 0.2-20; n is 2 to 10.

In the formula (III), R as a substituent on the aromatic ring represents a C1-C20 alkyl group, a C1-C20 alkoxy group or a C2-C20 unsaturated hydrocarbon group, and R 'as a substituent on the cyclohexane ring represents a C1-C20 alkyl group, a C1-C20 alkoxy group or a C2-C20 unsaturated hydrocarbon group, provided that the number of the substituents R or R' may be 1 to 5, and when the number of the substituents is 2 or more, the substituents may be the same as or different from each other, and may be located at any position; a, b, c and d represent the number of repeating units, and the repeating units may be connected in any order, and may be arranged in a block manner, alternately or randomly.

A preferred embodiment of the hydrogenated terpene aromatic resin may also be described as, for example, a resin containing a repeating unit of the formula (II) having a cyclohexyl group, provided that the resin may contain at least one repeating unit selected from the group consisting of a repeating unit represented by the formula (I) and a repeating unit represented by the following formula (IV) in the structure. The repeating units may be linked in any order and may be arranged in blocks, alternately or randomly.

In formula (IV), m and n represent the number of repeating units.

The hydrogenated terpene aromatic resin has a hydroxyl value (i.e., equivalent to the phenol group content) of 20mg KOH/g or less, preferably 10mg KOH/g or less, more preferably 5mg KOH/g or less, still more preferably 1mg KOH/g or less, and yet more preferably 0.1mg KOH/g or less. Particularly preferably 0mg KOH/g. If the hydroxyl value exceeds 20mg KOH/g, the resin may show an increase in self-aggregation, thereby decreasing the affinity for the rubber and the filler and failing to provide sufficient grip performance.

The hydroxyl value of the hydrogenated terpene aromatic resin means the amount (mg) of potassium hydroxide required for neutralizing acetic acid binding hydroxyl groups at the time of acetylation of 1g of the hydrogenated terpene aromatic resin, which is determined by potentiometric titration method (JIS K0070: 1992).

The softening point of the hydrogenated terpene aromatic resin is preferably 80 ℃ or more, more preferably 90 ℃ or more, further preferably 100 ℃ or more, further preferably 114 ℃ or more, particularly preferably 116 ℃ or more, and most preferably 120 ℃ or more. The softening point is preferably 180 ℃ or lower, more preferably 170 ℃ or lower, still more preferably 165 ℃ or lower, particularly preferably 160 ℃ or lower, and most preferably 135 ℃ or lower. Hydrogenated terpene aromatic resins having a softening point of less than 80 ℃ tend to be well dispersed in rubber but to lower grip performance, while hydrogenated terpene aromatic resins having a softening point of more than 180 ℃ tend to be poorly dispersed and thus fail to provide sufficient grip performance and also tend to fail to provide good durability.

Softening point of hydrogenated terpene aromatic resin according to JIS K6220-1: 2001, measured using a ball and ring softening point measuring device, which is defined as the temperature at which the ball falls.

The hydrogenated terpene aromatic resin preferably has a glass transition temperature (Tg) of 20 ℃ or higher, more preferably 30 ℃ or higher, and still more preferably 40 ℃ or higher. The Tg is preferably 100 ℃ or less, more preferably 90 ℃ or less, and still more preferably 80 ℃ or less.

Here, the glass transition temperature of the hydrogenated terpene aromatic resin was measured by Differential Scanning Calorimetry (DSC) at a temperature rise rate of 10 ℃/min in accordance with JIS K7121.

The weight average molecular weight (Mw) of the hydrogenated terpene aromatic resin is not particularly limited, but is preferably 300 to 3000, more preferably 500 to 2000, and still more preferably 600 to 2000. When Mw is less than 300, the G' value (hardness) of the adhesive layer tends to become low, resulting in insufficient grip performance, while when Mw is more than 3000, rubber hardness tends to increase, resulting in insufficient grip performance or durability.

Here, the weight average molecular weight of the hydrogenated terpene aromatic resin can be calibrated with polystyrene standards by Gel Permeation Chromatography (GPC) (GPC-8000 series available from Tosoh corporation, detector: differential refractometer, column: TSKGEL SUPERMALTPORE HZ-M, manufactured by Tosoh corporation).

The rubber composition of the present invention contains 1 to 50 parts by mass of a hydrogenated terpene aromatic resin per 100 parts by mass of a diene rubber. The content of the hydrogenated terpene aromatic resin is preferably 2 parts by mass or more, more preferably 3 parts by mass or more, and further preferably 5 parts by mass or more. The amount is also preferably 40 parts by mass or less, more preferably 35 parts by mass or less, and still more preferably 30 parts by mass or less. If the amount is less than 1 part by mass, gripping performance or durability tends to be insufficient. If it exceeds 50 parts by mass, the hardness (handling property) or fuel economy tends to be insufficient.

In the present invention, the difference in solubility parameter (SP value) between the diene rubber and the hydrogenated terpene aromatic resin is preferably 1.5 or less. When the difference in the SP value is within the above range, the compatibility of the diene rubber with the hydrogenated terpene aromatic resin becomes good, and thus the grip performance and durability are further improved. The difference in SP values is more preferably 1.0 or less. The lower limit of the difference in SP values is not particularly limited, but a smaller difference is more preferable.

The SP values of the diene rubber and the hydrogenated terpene aromatic resin are solubility parameters calculated using the Hoy method based on the structure of the compound. The calculation of the Hoy method is described, for example, in K.L.hoy, "Table of solubility parameters (Table of solubility parameters)", Solvent and Coatings Materials Research and development department, Union Carbits Corp. (1985).

The rubber composition of the present invention preferably contains at least one inorganic filler selected from the group consisting of a compound represented by the following formula, magnesium sulfate and silicon carbide.

mM·xSiO_y·zH₂O

In the formula, M represents at least one metal selected from the group consisting of Al, Mg, Ti, Ca and Zr or an oxide or hydroxide of the metal; m represents an integer of 1 to 5, x represents an integer of 0 to10, y represents an integer of 2 to 5, and z represents an integer of 0 to 10.

Examples of the compound in the above formula include alumina, hydrated alumina, aluminum hydroxide, magnesium oxide, talc, titanium white, titanium black, calcium oxide, calcium hydroxide, aluminum magnesium oxide, clay, pyrophyllite, bentonite, aluminum silicate, magnesium silicate, calcium aluminum silicate, magnesium silicate, zirconium and zirconia. These inorganic compounds may be used alone or in combination of two or more.

Inorganic fillers in which M is Al or Zr metal or an oxide or hydroxide of the metal are preferable because they have a mohs hardness of 3 or more, have water resistance and oil resistance, and when processed into micron-sized particles, they produce a scratch effect or promote blooming of an adhesive component providing grip performance, thereby improving grip performance, and they can also provide good processability, economic efficiency and foaming resistance. More preferred are aluminum hydroxide or zirconium oxide because they are abundant in resources and inexpensive. Aluminum hydroxide is particularly preferred because it further provides good compounding yield and good extrusion processability.

Nitrogen adsorption specific surface area (N) of inorganic filler₂SA) of 10 to 120m²(ii) in terms of/g. When N is present₂If SA is outside the above range, grip performance is reduced and wear resistance is reduced. N is a radical of₂The lower limit of SA is preferably 13m²In terms of/g, and N₂The upper limit of SA is preferably 115m²(ii) g, more preferably 110m²(ii) g, more preferably 80m²Per g, particularly preferably 70m²/g。

N of inorganic filler₂SA is determined by the BET method according to ASTM D3037-81.

The inorganic filler preferably has a linseed oil absorption of 30mL/100g or more, more preferably 35mL/100g or more. The linseed oil absorption is also preferably 75mL/100g or less, more preferably 50mL/100g or less, and particularly preferably 40mL/100g or less. When the linseed oil absorption is within the above range, the resulting pneumatic tire can exhibit excellent grip performance and excellent durability. A smaller linseed oil absorption results in less linkage (lower structure) between the inorganic filler particles, making the inorganic filler particles more likely to be present alone in the rubber. Accordingly, linseed oil absorption is considered to be an effective index for determining whether or not each inorganic filler particle in the nonpolar rubber composition for a tire is moderately fine and forms an aggregate of an intermediate secondary particle size. Specifically, if the linseed oil absorption is less than 30mL/100g, it is considered that the affinity for the rubber component, the softener, the resin and the like is reduced, so that the position of the inorganic filler in the rubber composition is thermally unstable. Further, if the linseed oil absorption exceeds 75mL/100g, the inorganic filler particles form aggregates having a large secondary particle diameter, the inside of which forms a closed portion containing oil, or cannot be sufficiently mixed with the rubber component even after the kneading process, thereby causing deterioration in abrasion resistance, durability, or other properties. Furthermore, DBP oil absorption is commonly used in the art, but linseed oil, as a natural oil, has another advantage in that it brings less environmental load than DBP.

For reference, ULTRASIL VN3 (available from Evonik, N.)₂SA：175m²/g) as a typical wet silica (in which the particle structure is easily grown) has a linseed oil absorption of 128mL/100 g.

The oil absorption of linseed oil is measured in accordance with JIS K5101-13.

The average particle diameter of the inorganic filler is preferably 1.5 μm or less, more preferably 0.69 μm or less, and still more preferably 0.6 μm or less. The average particle diameter is also preferably 0.2 μm or more, more preferably 0.25 μm or more, and still more preferably 0.4 μm or more. When it is more than 1.5 μm, grip performance may be reduced and durability may be deteriorated. The inorganic filler having an average particle diameter of less than 0.2 μm is liable to form secondary aggregates in the rubber, disadvantageously resulting in a decrease in grip performance and a decrease in durability.

The average particle diameter of the inorganic filler is a number average particle diameter measured by a transmission electron microscope.

In order to ensure the grip performance and durability of the tire and reduce metal abrasion of the Banbury mixer and the extruder, the Mohs hardness of the inorganic filler is preferably 7 or less than 7, more preferably 2 to 5, based on silica.

Mohs hardness, one of the mechanical properties of a material, is a measure that has been commonly used in the field of minerals for many years. The mohs hardness is measured by scratching a material to be analyzed for hardness (e.g., aluminum hydroxide) with a reference material and then checking whether there is a scratch.

It is particularly preferable to use an inorganic filler having a Mohs hardness of less than 7 and a dehydrated product thereof having a Mohs hardness of 8 or more. For example, the use of aluminum hydroxide having a Mohs hardness of about 3 can prevent abrasion (breakage) of the Banbury mixer and the rolls. Further, the outer surface layer of aluminum hydroxide undergoes dehydration reaction (transformation) due to vibration or heat accumulation during middle and late stages of running and partially due to kneading, and thus is transformed into alumina having a mohs hardness of about 9, which is the same as or harder than stone hardness on roads, with the result that good grip performance and durability can be obtained. The internal aluminum hydroxide need not be fully converted and partial conversion may provide a road scraping effect. In addition, aluminum hydroxide and alumina are stable to water, alkali and acids, and neither inhibit sulfidation nor promote oxidative degradation. The converted inorganic filler more preferably has a mohs hardness of 7 or more, which has no upper limit. The diamond has the highest hardness of 10.

The inorganic filler preferably has a thermal decomposition initiation temperature (DSC endothermic initiation temperature) of 160 to 500 ℃ and more preferably 170 to 400 ℃. In the case where the thermal decomposition starting temperature is less than 160 ℃, the inorganic filler may be excessively thermally decomposed or re-aggregated during the kneading process, so that the metals of the rotor blades, the vessel walls, etc. of the kneader are excessively worn. The thermal decomposition onset temperature of the inorganic filler is determined by Differential Scanning Calorimetry (DSC). Thermal decomposition involves dehydration reactions.

The inorganic filler may have the above-mentioned N₂Commercially available products in the SA range may also be inorganic filler particles processed, for example by grinding or other treatment, to have the properties described above. The grinding treatment may be carried out by a conventional method, for example, wet grinding or dry grinding using, for example, a jet mill, a fluid jet mill, a back jet mill or a reverse phase mill (a cascade mill).

Having a predetermined N, if desired₂The inorganic filler of SA can be prepared by fractionation by a membrane filtration method widely used in the medical or biotechnological fields before being used as a compounding agent for rubber.

The amount of the inorganic filler is 1 part by mass or more, preferably 3 parts by mass or more, and more preferably 5 parts by mass or more, relative to 100 parts by mass of the diene rubber. When the inorganic filler is less than 1 part by mass, grip performance (particularly wet grip performance) may be insufficient. The amount is 70 parts by mass or less, preferably 60 parts by mass or less, more preferably 50 parts by mass or less, and still more preferably 40 parts by mass or less. An amount exceeding 70 parts by mass results in insufficient dispersion of the filler, and thus poor grip performance (particularly dry grip performance) or abrasion resistance.

Particularly when used in a passenger car tire, the amount of the inorganic filler is preferably 10 to 20 parts by mass relative to 100 parts by mass of the diene rubber to achieve both grip performance and abrasion resistance.

The rubber composition of the present invention preferably contains carbon black to provide reinforcement, grip and protection against Ultraviolet (UV) induced degradation.

Nitrogen adsorption specific surface area (N) of carbon black₂SA) is preferably 100m²(ii) g or more, more preferably 110m²(ii) g or more, and more preferably 115m²A total of 140m or more, particularly preferably²(ii) a ratio of/g or more. N is a radical of₂SA is also preferably 600m²(ii) g or less, more preferably 500m²(ii) g or less, more preferably 400m²(ii) per gram or less. When it is less than 100m²At/g, grip performance or abrasion resistance tends to be lowered. When it exceeds 600m²At/g, good filler dispersion is hardly likely to occur, and thus reinforcing properties or durability tends to deteriorate. N of carbon black₂SA was determined by the method according to JIS K6217-2: 2001 by the BET method.

The amount of carbon black varies depending on the grip performance, abrasion resistance or fuel economy required for the tire. In order to prevent Ultraviolet (UV) -induced cracking, the content of carbon black is preferably 5 parts by mass or more with respect to 100 parts by mass of the diene rubber. When silica is used to ensure wet grip performance, the amount of carbon black is about 5 to 50 parts by mass relative to 100 parts by mass of the diene rubber. When carbon black is used to ensure dry grip performance and abrasion resistance, the content of carbon black is preferably 50 to 160 parts by mass with respect to 100 parts by mass of the diene rubber.

The rubber composition of the present invention may contain silica. The incorporation of silica improves rolling resistance performance while enhancing wet grip performance and reinforcing performance. This is a significant synergistic effect obtained by the combined use with the specific inorganic filler in the present invention, which is probably due to the above-described mechanisms (1) and (B).

Examples of silica include those produced by wet or dry processes.

Nitrogen adsorption specific surface area (N) of silica₂SA) is preferably 80m²(ii) g or more, more preferably 120m²(ii) g or more, more preferably 150m²(ii) a ratio of/g or more. N is a radical of₂SA is also preferably 280m²(ii) g or less, more preferably 260m²(ii) g or less, more preferably 250m²(ii) per gram or less.

N of silicon dioxide₂SA is determined by the BET method according to ASTM D3037-93.

In applications where wet grip performance is more important than dry grip performance, the content of silica is preferably 30 parts by mass or more, more preferably 60 parts by mass or more, further preferably 75 parts by mass or more, further preferably 85 parts by mass or more, and particularly preferably 90 parts by mass or more, per 100 parts by mass of the diene rubber. When it is less than 30 parts by mass, sufficient reinforcing properties cannot be obtained. The amount is also preferably 150 parts by mass or less, more preferably 130 parts by mass or less, still more preferably 120 parts by mass or less, and particularly preferably 100 parts by mass or less. When it exceeds 150 parts by mass, silica is difficult to disperse, and therefore abrasion resistance, durability or fuel economy tends to deteriorate.

When the rubber composition of the present invention contains silica, it preferably further contains a silane coupling agent. The silane coupling agent may be any silane coupling agent commonly used with silica in the rubber industry.

In another suitable embodiment of the present invention, the rubber composition of the present invention further contains a softening agent in view of grip performance and other properties. Any softening agent may be used, including oils, liquid diene polymers and resins having a softening point of 160 ℃ or less. In particular, the softener preferably contains oil and a liquid diene polymer, and in a suitable embodiment of the present invention, the softener further includes a resin having a softening point of 160 ℃ or less in view of grip performance.

Examples of oils include process oils such as paraffinic process oils, aromatic process oils, and naphthenic process oils. Particularly preferred are oils having a smaller difference in solubility parameter (SP value) than diene rubbers. Oils with smaller differences in SP values are better miscible with diene rubbers. The difference in SP values is preferably, for example, 1.0 or less. The lower limit of the difference in SP values is not particularly limited, but more preferably has a smaller difference.

The SP value of the oil was measured as described above for the diene rubber and hydrogenated terpene aromatic resin.

When the oil is added, the amount of the oil is preferably 2 parts by mass or more, more preferably 5 parts by mass or more, relative to 100 parts by mass of the diene rubber, although the amount varies depending on the grip performance and fuel economy required for the tire or the filler content. The amount of the oil is preferably 85 parts by mass or less, more preferably 75 parts by mass or less. With less than 2 parts by mass of oil, poor dispersion of fillers, polymers or crosslinking agents such as sulfur may occur. When the oil is used in excess of 85 parts by mass, the durability or wear resistance tends to deteriorate.

The amount of oil used in the present invention includes the amount of oil contained in the oil-extended rubber.

It should be noted that truck and bus tires requiring high abrasion, durability and cut resistance are generally free of oil.

The term "liquid diene polymer" means a diene polymer that is liquid at room temperature (25 ℃).

The liquid diene polymer preferably has a weight average molecular weight (Mw) of 1.0X 10 in terms of polystyrene as measured by Gel Permeation Chromatography (GPC)³～2.0×10⁵More preferably 3.0X 10³～1.5×10⁴. Mw less than 1.0X 10³The liquid diene polymer of (2) is not effective in improving grip performance and sufficient durability cannot be secured, and Mw is more than 2.0X 10⁵The liquid diene polymer of (a) may form an excessively viscous polymer solution, resulting in a decrease in yield, or may decrease in fracture properties.

The Mw of the liquid diene polymers used in the present invention is determined by Gel Permeation Chromatography (GPC) calibrated with polystyrene standards.

Examples of the liquid diene polymer include a liquid styrene-butadiene copolymer (liquid SBR), a liquid polybutadiene polymer (liquid BR), a liquid polyisoprene polymer (liquid IR) and a liquid styrene-isoprene copolymer (liquid SIR). Among them, liquid SBR is preferable because a good balance of durability and grip performance can be obtained.

When the liquid diene polymer is added, the amount of the liquid diene polymer is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, relative to 100 parts by mass of the diene rubber. The amount is also preferably 120 parts by mass or less, more preferably 80 parts by mass or less, still more preferably 70 parts by mass or less, and particularly preferably 30 parts by mass or less. When the liquid diene polymer is less than 5 parts by mass, sufficient grip performance cannot be obtained. When the liquid diene polymer exceeds 120 parts by mass, the durability tends to deteriorate.

Examples of resins having a softening point of 160 ℃ or less that can be used in combination with the hydrogenated terpene aromatic resin of the present invention include coumarone-indene resins, p-tert-butylphenol acetylene resins and styrene-acrylic resins.

The term "coumarone-indene resin" means a resin containing coumarone and indene as monomer components forming the skeleton (main chain) of the resin the main chain of the resin may contain, in addition to coumarone and indene, monomer components such as styrene, α -methylstyrene, methylindene, or vinyltoluene.

The coumarone-indene resin has a softening point of-20 ℃ to 160 ℃. The upper limit of the softening point thereof is preferably 145 ℃ or less, more preferably 130 ℃ or less. The lower limit thereof is preferably-10 ℃ or more, more preferably-5 ℃ or more. Coumarone-indene resins having a softening point higher than 160 ℃ exhibit poor dispersibility during kneading, resulting in a decrease in fuel economy. Coumarone-indene resins with softening points less than-20 ℃ are difficult to prepare and are more likely to migrate to other components and volatilize, which may lead to changes in properties during use.

When the coumarone-indene resin used has a softening point of 90 ℃ to 140 ℃, the grip performance is improved. Particularly, the coumarone-indene resin having a softening point of 100 to 120 ℃ can improve tan delta in the range of 0 to 80 ℃ as a whole, and has good durability.

When the coumarone-indene resin used has a softening point of 10 ℃ to 30 ℃, it has good grip performance at relatively low temperatures between 10 ℃ and 40 ℃ and generally decreases tan δ. The coumarone-indene resin having a softening point of 10 to 30 ℃ is mainly used for improving durability.

The mechanism for improving durability by using coumarone-indene resins may be that the coumarone-indene resins impart moderate sliding properties to the crosslinked polymer chains, allowing them to elongate uniformly.

The softening point of the coumarone-indene resin used in the present invention is in accordance with JIS K6220-1: 2001 was measured using a ball and ring softening point measuring device, which is defined as the temperature at which the ball fell.

The softening point of the resin is preferably 120 ℃ to 160 ℃ (for example, Koresin with softening point of 145 ℃), the mixing of the p-tert-butylphenol acetylene resin improves the gripping performance, especially at high temperature (about 80 ℃ to 120 ℃), and the combination of Koresin and α -methylstyrene resin with softening point of about 85 ℃ can provide excellent gripping performance at low temperature (10 ℃ to 40 ℃) so as to improve the gripping performance when the driving temperature of the tire is between 20 ℃ and 120 ℃.

The softening point of p-tert-butylphenol acetylene resin can be determined as described for coumarone-indene resin.

The hydroxyl value of the p-tert-butylphenol acetylene resin is preferably 100mg KOH/g or more, more preferably 150mg KOH/g or more, and still more preferably 175mg KOH/g or more. The hydroxyl value is also preferably 300mg KOH/g or less, more preferably 250mg KOH/g or less, and still more preferably 200mg KOH/g or less.

The hydroxyl value of the p-tert-butylphenol acetylene resin can be measured as described for the hydrogenated terpene aromatic resin.

In addition to the above-mentioned components, the rubber composition of the present invention may suitably contain compounding agents which are generally used in the tire industry, such as wax, zinc oxide, stearic acid, mold release agents, antioxidants, vulcanizing agents such as sulfur and vulcanization accelerators, and the like.

Any zinc oxide may be used in the present invention, including, for example, those used in the rubber field in tires. For better dispersion of zinc oxide and higher wear resistance, the zinc oxide may suitably be a finely dispersed zinc oxide. Specifically, the average primary particle diameter of zinc oxide is preferably 200nm or less, more preferably 100nm or less. The lower limit of the average primary particle diameter is not particularly limited, but is preferably 20nm or more, and more preferably 30nm or more.

The average primary particle diameter of zinc oxide means an average particle diameter (average primary particle diameter) calculated from a specific surface area measured by a BET method based on nitrogen adsorption. The zinc oxide preferably has a particle size of 10 to 50m as determined by the BET method based on nitrogen adsorption²Specific surface area per gram (N)₂SA)。

When zinc oxide is mixed, the content of zinc oxide is preferably 0.5 to10 parts by mass or less, more preferably 1 to 5 parts by mass, per 100 parts by mass of the diene rubber. When the amount of zinc oxide is within the above range, the effects of the present invention can be more suitably achieved.

Examples of the vulcanization accelerator usable in the present invention include a sulfenamide-based vulcanization accelerator, a thiazole-based vulcanization accelerator, a thiuram-based vulcanization accelerator, a guanidine-based vulcanization accelerator and a dithiocarbamate-based vulcanization accelerator. These vulcanization accelerators may be used alone or in combination of two or more. Among them, the sulfenamide-based vulcanization accelerator, the thiuram-based vulcanization accelerator, the guanidine-based vulcanization accelerator and the dithiocarbamate-based vulcanization accelerator are suitable for the present invention, and a combination of the sulfenamide-based vulcanization accelerator and the guanidine-based vulcanization accelerator is particularly preferable.

Examples of sulfenyl amine vulcanization accelerators include N-tert-butyl-2-benzothiazole sulfenamide (TBBS), N-cyclohexyl-2-benzothiazole sulfenamide (CBS) and N, N-dicyclohexyl-2-benzothiazole sulfenamide (DCBS).

Examples of the thiuram-based vulcanization accelerator include tetramethylthiuram disulfide (TMTD), tetrabenzylthiuram disulfide (TBzTD) and tetrakis (2-ethylhexyl) thiuram disulfide (TOT-N).

Examples of the guanidine-based vulcanization accelerator include Diphenylguanidine (DPG), di-o-tolylguanidine and o-tolylbiguanide.

Examples of the dithiocarbamate-based vulcanization accelerator include zinc dibenzyldithiocarbamate (ZTC) and zinc ethylphenyldithiocarbamate (PX).

When the vulcanization accelerator is added, the amount of the vulcanization accelerator is preferably 1 part by mass or more, more preferably 2 parts by mass or more, but preferably 15 parts by mass or less, more preferably 10 parts by mass or less, relative to 100 parts by mass of the diene rubber. An amount of the vulcanization accelerator less than 1 part by mass tends to fail to provide a sufficient vulcanization rate, resulting in failure to obtain good grip performance or durability. An amount thereof exceeding 15 parts by mass may result in excessively high crosslinking density or excessive blooming, resulting in a decrease in grip performance, durability or molding tackiness.

The rubber composition for a tread of the present invention can be prepared by a conventional method.

For example, first, the components containing no sulfur or vulcanization accelerator are added (mixed) to a rubber mixer such as a banbury mixer or an open roll mill and kneaded to obtain a kneaded product (basic kneading step). Subsequently, sulfur and a vulcanization accelerator are further mixed (added) into the kneaded mixture and kneaded, followed by vulcanization, whereby a rubber composition can be prepared.

The basic mixing step is not particularly limited as long as the rubber component containing the diene rubber and other components is mixed. The basic mixing step may be carried out in a single step, or may be divided into two steps in which the rubber component is previously mixed with some components including the hydrogenated terpene aromatic resin, and then the mixture is mixed with other components excluding sulfur and a vulcanization accelerator.

The rubber composition is used in a tread of a pneumatic tire, and is particularly suitable for a cap tread forming an outer surface layer of a tread having a multilayer structure. The rubber composition is suitable for use in, for example, the outer surface layer of a tread having a two-layer structure consisting of an outer surface layer (cap tread) and an inner surface layer (base tread).

The pneumatic tire of the present invention can be produced from the above rubber composition by a conventional method.

Specifically, a rubber composition containing the above-mentioned components before vulcanization is extruded into a tread shape, and then assembled with other tire components in a usual manner on a tire building machine to produce an unvulcanized tire. The unvulcanized tire is hot-pressed in a vulcanizer to produce a tire.

The pneumatic tire of the present invention is suitable for heavy vehicles such as passenger cars, large buses, large SUVs, trucks and buses, light trucks, and particularly preferably for passenger cars. Pneumatic tires may be used as summer tires or studless winter tires for those vehicles.

Examples

The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

The chemicals used in the examples and comparative examples are listed below.

<SBR>

Modified SBR1 for silica: a product (oil extended [ oil content: 37.5 parts by mass per 100 parts by mass of rubber solid ] prepared as described below]The styrene content: 41 mass%, vinyl content: 40 mass%, glass transition temperature: -29 ℃, weight average molecular weight: 1190000, SP value: 8.60)

N9548: nipol 9548(E-SBR, oil extended [ oil content: 37.5 parts by mass per 100 parts by mass of rubber solids ], styrene content: 35 mass%, vinyl content: 18 mass%, glass transition temperature: -40 ℃, weight average molecular weight: 1090000, SP value: 8.50) available from Zeon corporation

Modified SBR2 for silica: the product (non-oil-extended, styrene content: 27% by mass, vinyl content: 58% by mass, glass transition temperature: -27 ℃, weight-average molecular weight: 720000, SP value: 8.55)

NS612: nipol NS612(S-SBR, non-oil-extended, styrene content: 15 mass%, vinyl content: 30 mass%, glass transition temperature: -65 ℃, weight-average molecular weight: 780000, SP value: 8.40) available from Zeon corporation

<BR>

CB25: BUNA-CB25 (rare earth-catalyzed BR synthesized using Nd catalyst, vinyl content: 0.7 mass%, cis content: 97 mass%, glass transition temperature: -110 ℃ and SP value: 8.20) available from Lanxess

<NR>

TSR20(SP value: 8.10)

< carbon Black >

HP180：HP180(N₂SA：175m²/g), available from Orion Engineered carbon Inc

< silica >

VN3：ULTRASIL VN3(N₂SA：175m²(g), linseed oil absorption: 128mL/100g) from Evonik

< aluminum hydroxide >

Aluminum hydroxide 1: Wet-Synthesis of the product (average particle diameter: 2.7 μm, N)₂SA：274m²(g), linseed oil absorption: 104mL/100g, Mohs hardness: 3, mohs hardness of its pyrolysate (alumina): 9, thermal decomposition start temperature: 200 ℃ C.), purchased from Hutian industries Co Ltd

Aluminum hydroxide 2: Wet-Synthesis of the product (average particle diameter: 2.7 μm, N)₂SA：122m²(g), linseed oil absorption: 78mL/100g, Mohs hardness: 3, mohs hardness of its pyrolysate (alumina): 9, thermal decomposition start temperature: 200 ℃ C.), purchased from Hutian industries Co Ltd

Aluminum hydroxide 3: dry-milled product of ATH # B (average particle diameter: 0.5 μm, N)₂SA：95m²(g), linseed oil absorption: 42mL/100g, Mohs hardness: 3, mohs hardness of its pyrolysate (alumina): 9, thermal decomposition start temperature: 200 ℃ C.), purchased from Sumitomo chemical Co., Ltd

Aluminum hydroxide 4: dry grind product of ATH # B (average)Particle size: 0.5 μm, N₂SA：75m²(g), linseed oil absorption: 42mL/100g, Mohs hardness: 3, mohs hardness of its pyrolysate (alumina): 9, thermal decomposition start temperature: 200 ℃ C.), purchased from Sumitomo chemical Co., Ltd

Aluminum hydroxide 5: dry-milled product of ATH # B (average particle diameter: 0.3 μm, N)₂SA：35m²(g), linseed oil absorption: 37mL/100g, Mohs hardness: 3, mohs hardness of its pyrolysate (alumina): 9, thermal decomposition start temperature: 200 ℃ C.), purchased from Sumitomo chemical Co., Ltd

Aluminum hydroxide 6: ATH # B (average particle diameter: 0.6 μm, N)₂SA：15m²(g), linseed oil absorption: 40mL/100g, Mohs hardness: 3, a pyrolysate thereof ((Mohs hardness of alumina: 9, thermal decomposition initiation temperature: 200 ℃ C.), available from Sumitomo chemical Co., Ltd.)

Aluminum hydroxide 7: HIGILITE H-43 (average particle diameter: 0.75 μm, N)₂SA：7m²(g), linseed oil absorption: 33mL/100g, Mohs hardness: 3, mohs hardness of its pyrolysate (alumina): 9, thermal decomposition start temperature: 200 ℃ C., available from Showa Denko K.K

< terpene-based resin >

M125: YS polyester M125 (degree of hydrogenation: 11%, softening point: 123 ℃, Tg: 69 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.52) from Yasuhara Chemical Co., Ltd

M115: YS polyester M115 (degree of hydrogenation: 12%, softening point: 115 ℃, Tg: 59 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.52) from Yasuhara Chemical Co., Ltd

M105: YS polyester M105 (degree of hydrogenation: 12%, softening point: 105 ℃, Tg: 48 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.52) from Yasuhara Chemical Co., Ltd

M80: YS polyester M80 (degree of hydrogenation: 12%, softening point: 80 ℃, Tg: 23 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.52) from Yasuhara Chemical Co., Ltd

1 to 4 resins: the resin was prepared as follows

TO125: YS resin TO125 (aromatic modified terpene resin, degree of hydrogenation: 0%, softening point: 125 ℃, Tg: 64 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.73) commercially available from Yasuhara Chemical Co., Ltd

TO115: YS resin TO115 (aromatic modified terpene resin, degree of hydrogenation: 0%, softening point: 115 ℃, Tg: 54 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.73) purchased from Yasuhara Chemical Co., Ltd

TO105: YS resin TO105 (aromatic modified terpene resin, degree of hydrogenation: 0%, softening point: 105 ℃, Tg: 45 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.73) commercially available from Yasuhara Chemical Co., Ltd

TO85: YS resin TO85 (aromatic modified terpene resin, degree of hydrogenation: 0%, softening point: 85 ℃, Tg: 25 ℃, hydroxyl value: 0mg KOH/g, SP value: 8.73) from Yasuhara Chemical Co., Ltd

T160: YS polyester T160 (terpene phenolic resin, degree of hydrogenation: 0%, softening point: 160 ℃, Tg: 100 ℃, hydroxyl value: 60mg KOH/g, SP value: 8.81) from Yasuhara Chemical Co., Ltd

G125: YS polyester G125 (terpene phenol resin, degree of hydrogenation: 0%, softening point: 125 ℃, Tg: 67 ℃, hydroxyl value: 140mg KOH/G, SP value: 9.07) available from Yasuhara Chemical Co., Ltd

TP115: sylvares TP115 (terpene phenolic resin, degree of hydrogenation: 0%, softening point: 115 ℃, Tg: 55 ℃, hydroxyl number: 50mg KOH/g, SP value: 8.77) available from Arizona Chemical

< Petroleum-derived resin >

Koresin: dry grinding of Koresin (P-tert-butylphenol acetylene resin [ condensation resin of P-tert-butylphenol and acetylene ]]The softening point: 145 ℃, Tg: 98 ℃, hydroxyl value: 193mg KOH/g, N₂SA：4.1m²G, SP value: 9.10) from BASF

V-120: nitto resin coumarone V-120 (coumarone-indene resin, softening point: 120 ℃, hydroxyl value: 30mg KOH/g, SP value: 9.00) purchased from Nippo Chemicals K.K

SA85SYLVARES SA85(α -methyl phenethyl ether)Ethylenic resin [ α -copolymer of methylstyrene and styrene]The softening point: 85 ℃, Tg: 43 ℃, hydroxyl value: 0mg KOH/g, SP value: 9.10) available from Arizona Chemical

< oil >

AH-24: diana Process AH-24(SP value: 8.05) from Kyohima K.K

< liquid diene Polymer >

L-SBR-820: L-SBR-820 (liquid SBR, Mw: 10,000), available from Kuraray corporation

< silane coupling agent >

Si75: silane coupling agent Si75 (bis (3-triethoxysilylpropyl) disulfide), available from Evonik

< waxes >

Ozoace 355: ozoace 355 from Japan wax Co., Ltd

< antioxidant >

6PPD: antigene 6C (N-phenyl-N' - (1, 3-dimethyl) p-phenylenediamine) available from Sumitomo chemical Co., Ltd

TMQ: NORAC 224(2,2, 4-trimethyl-1, 2-dihydroquinoline polymer) available from New chemical industries, Inc. in Dali

< stearic acid >

Stearic acid: stearic acid "TSUBAKI" available from Nichioil Co., Ltd

< Zinc oxide >

Zinc oxide #2: zinc oxide #2 from Mitsui Metal mining, Inc

< vulcanizing agent >

Powdered sulfur containing 5% oil: HK-200-5 available from Mitsui chemical industries, Inc

< vulcanization accelerators >

DPG: NOCCELER D (N, N-diphenylguanidine), available from New chemical industries, Inc. in the interior

TBBS: NOCCELER NS-G (N-tert-butyl-2-benzothiazolyl-sulfenamide), available from New chemical industries, Inc

Preparation of chain end modifier for SBR

To a 250mL measuring flask, 20.8g of 3- (N, N-dimethylamino) propyltrimethoxysilane (available from AZmax. K.) was added under a nitrogen atmosphere, and then anhydrous hexane (available from Kanto chemical Co., Ltd.) was added to make the total volume 250mL, thereby preparing a chain end modifier.

Preparation of modified SBR1 for silica

To a 30L pressure resistant vessel which had been fully purged with nitrogen gas were charged 18L of n-hexane, 800g of styrene (available from Kanto chemical Co., Ltd.), 1200g of butadiene and 1.1mmol of tetramethylethylenediamine, and the temperature was raised to 40 ℃. Then, 1.8mL of 1.6M butyllithium (purchased from Kanto chemical Co., Ltd.) was added to the mixture, and the mixture was heated to 50 ℃ and stirred for 3 hours. Subsequently, 4.1mL of chain end modifier was added to the resulting mixture, followed by stirring for 30 minutes. To the reaction solution were added 15mL of methanol and 0.1g of 2, 6-t-butyl-p-cresol (available from Dainiji New chemical industries Co., Ltd.), followed by addition of 1200g of TDAE, followed by stirring for 10 minutes. Thereafter, the coagulum was recovered from the polymer solution by steam stripping. The condensate was dried under reduced pressure for 24 hours to obtain modified SBR No. 1 for silica.

Preparation of modified SBR2 for silica

To a 30L pressure resistant vessel which had been fully purged with nitrogen gas were charged 18L of n-hexane, 740g of styrene (available from Kanto chemical Co., Ltd.), 1260g of butadiene and 10mmol of tetramethylethylenediamine, and the temperature was raised to 40 ℃. Then, 10mL of butyllithium was added to the mixture, and the mixture was warmed to 50 ℃ and then stirred for 3 hours. Subsequently, 11mL of the chain end modifier was added to the resulting mixture, followed by stirring for 30 minutes. To the reaction solution were added 15mL of methanol and 0.1g of 2, 6-t-butyl-p-cresol. The reaction solution was then placed in a stainless steel vessel containing 18L of methanol, and the coagulum was recovered therefrom. The condensate was dried under reduced pressure for 24 hours to obtain modified SBR2 for silica.

Synthesis of hydrogenated terpene aromatic resins

(Synthesis of resin 1)

To a 3L autoclave equipped with stirring blades and purged sufficiently with nitrogen was added 1L of cyclohexane1L of Tetrahydrofuran (THF), 200g of a base resin (production batch TO125[ YS resin TO125, from Yasuhara Chemical Co., Ltd.)]The softening point was determined to be 127 ℃ C.) and 10g of 10% palladium on carbon. The autoclave was purged with nitrogen and then pressurized to 5.0kg/cm with hydrogen²And then catalytically hydrogenated at 80 ℃ for 0.5 hour to obtain resin 1. The yield was about 100%.

In order TO determine the degree of hydrogenation of the double bonds of the resin 1, a resin (non-hydrogenated TO125 or hydrogenated resin 1) was added TO carbon tetrachloride as a solvent at a concentration of 15 mass%, the mixture was subjected TO a 100MHz proton NMR test, and then the degree of hydrogenation of the double bonds was calculated from the degree of decrease in the spectral intensity corresponding TO the unsaturated bonds (the degree of hydrogenation was determined in the same manner below). As a result, the degree of hydrogenation of the double bonds (hydrogenation rate) of the resin 1 was found to be about 2%. The hydroxyl value (OH value), softening point and SP value of resin 1 were 0mgKOH/g, 123 ℃ and 8.70, respectively.

(Synthesis of resin 2)

Resin 2 was prepared as described above for "Synthesis of resin 1", but catalytic hydrogenation was carried out for only 1 hour. The yield almost reaches 100%. The results showed that the degree of hydrogenation of the double bonds, the hydroxyl number, the softening point and the SP value of resin 2 were about 5%, 0mg KOH/g, 123 ℃ and 8.68, respectively.

(Synthesis of resin 3)

Resin 3 was prepared as described above for "Synthesis of resin 1", but catalytic hydrogenation was carried out for 2 hours. The yield almost reaches 100%. As a result, it was found that the degree of hydrogenation of the double bonds, the hydroxyl value, the softening point and the SP value of resin 3 were about 8%, 0mg KOH/g, 124 ℃ and 8.60, respectively.

(Synthesis of resin 4)

Resin 4 was prepared as described above for "Synthesis of resin 1", but catalytic hydrogenation was carried out for 4 hours. The yield almost reaches 100%. As a result, it was found that the degree of hydrogenation of the double bonds, the hydroxyl value, the softening point and the SP value of the resin 4 were about 20%, 0mg KOH/g, 127 ℃ and 8.48, respectively.

The synthesis conditions, physical properties and other items of resins 1 TO 4 and TO125 and M125 are summarized in table 1 below.

[ Table 1]

	Degree of hydrogenation (%)	SP value	Reaction time (hours)	Softening Point (. degree. C.)	Yield (%)
						Resin 1	2	8.70	0.5	123	100
Resin 2	5	8.68	1	123	100
						Resin 3	8	8.60	2	124	100
Resin 4	20	8.48	4	127	100
						TO125	0	8.73	(produced by the manufacturer)	125	-
M125	11	8.52	(produced by the manufacturer)	123	-

< examples and comparative examples >

According to each formulation shown in Table 2, the compounding ingredients other than sulfur and a vulcanization accelerator were kneaded for 5 minutes at a discharge temperature of 150 ℃ using a 4.0L Banbury mixer manufactured by Kobe Steel Co. Then, sulfur and a vulcanization accelerator were added to the kneaded mixture, and they were kneaded for 4 minutes at a discharge temperature of 95 ℃ using an open roll mill to obtain an unvulcanized rubber composition.

The unvulcanized rubber composition was press-vulcanized at 160 ℃ for 20 minutes to obtain a vulcanized rubber composition.

Further, the unvulcanized rubber composition was extruded into a tread shape, assembled with other tire components on a tire building machine, and then vulcanized at 160 ℃ for 20 minutes to obtain a test tire (tire size: 215/45R17 summer, passenger car tire).

The vulcanized rubber composition and the test tire prepared as described above were subjected to the following evaluations. Table 2 shows the results.

The term "softening point of terpene-based resin" is calculated from the softening point and percentage of the constituent polymer. The items "SP value of diene rubber" and "SP value of terpene-based resin" were calculated from the SP value and percentage of the constituent polymer.

(Dry grip Performance)

The test tires were mounted on a 2000cc displacement front engine, rear wheel drive vehicle manufactured in japan. The test driver drives the car around the test track for 10 revolutions under dry asphalt pavement conditions and then evaluates the stability of the steering control. The results are expressed as an index, with comparative example 1 set to 100. A higher index indicates better dry grip performance.

(Wet grip Performance)

The test tires were mounted on a 2000cc displacement front engine, rear wheel drive vehicle manufactured in japan. The test driver drives the car around the test track for 10 turns under wet asphalt pavement conditions, and then evaluates the stability of the steering control. The results are expressed as an index, with comparative example 1 set to 100. A higher index indicates better wet grip performance.

The target value of the dry grip performance index or the wet grip performance index is 103 or more on average.

(tensile test)

The dumbbell No. 3 test pieces prepared from each of the vulcanized rubber compositions were subjected to a tensile test at room temperature in accordance with JIS K6251 "determination of vulcanized rubber or thermoplastic rubber-tensile stress-strain characteristics" to determine elongation at break EB (%). The EB value is expressed as an index, with comparative example 1 set to 100. A higher index indicates better durability.

[ Table 2]

(Next page continuation table 2)

The results shown in Table 2 show that when a mixture containing a predetermined amount of a hydrogenated terpene aromatic resin (having a degree of hydrogenation of double bonds of 5 to 100% and a hydroxyl value of 20mgKOH/g or less) obtained by hydrogenating double bonds of a terpene aromatic resin and a predetermined amount of a nitrogen adsorption specific surface area of 10 to 120m²In the specific inorganic filler examples of the present invention, the wet grip performance, dry grip performance and durability are greatly improved while maintaining a good balance therebetween.

In addition, it was found that improvements in performance can be achieved regardless of the amount of SBR, BR or NR in the polymer system and the amount of carbon black or silica in the filler system.

Claims (6)

1. A pneumatic tire having a tread made of a rubber composition,

the rubber composition contains a rubber component containing 90% by mass or more of a diene rubber based on 100% by mass of the rubber component,

the rubber composition further contains a hydrogenated terpene aromatic resin obtained by hydrogenating the double bond of the terpene aromatic resin,

the hydrogenated terpene aromatic resin has a degree of double bond hydrogenation of 5 to 100% and a hydroxyl value of 20mg KOH/g or less,

the content of the hydrogenated terpene aromatic resin is 1 to 50 parts by mass per 100 parts by mass of the diene rubber,

the rubber composition also contains nitrogen with the specific surface area of 10-120 m²(ii) an inorganic filler comprising at least one selected from the group consisting of a compound represented by the following formula, magnesium sulfate and silicon carbide,

the content of the inorganic filler is 1 to 70 parts by mass relative to 100 parts by mass of the diene rubber,

mM·xSiO_y·zH₂O

wherein M represents an oxide or hydroxide of at least one metal selected from the group consisting of Al, Mg, Ti, Ca and Zr; m represents an integer of 1 to 5, x represents an integer of 0 to10, y represents an integer of 2 to 5, and z represents an integer of 0 to 10.

2. The pneumatic tire of claim 1, wherein the inorganic filler is aluminum hydroxide.

3. The pneumatic tire according to claim 1 or 2, wherein the hydrogenated terpene aromatic resin has a softening point of 80 ℃ to 180 ℃.

4. The pneumatic tire according to claim 3, wherein the hydrogenated terpene aromatic resin has a softening point of 114 to 160 ℃.

5. The pneumatic tire according to claim 1 or 2, wherein the hydroxyl value of the hydrogenated terpene aromatic resin is 0mg KOH/g.

6. The pneumatic tire according to claim 1 or 2, wherein the diene rubber contains 60% by mass or more of a styrene-butadiene rubber having a styrene content of 19% by mass to 60% by mass.